Scaling-down the size of each memory cell is effective in realizing a lower bit cost and improving the memory performance of a nonvolatile semiconductor memory device. However, scaling-down of memory cells is becoming technically difficult.
In view of this, the use of organic molecules in charge storage layers has been suggested. With organic molecules, it is possible to achieve organic syntheses of various molecular structures and substituent groups. Because of this, desired electrochemical characteristics can be provided, and each structural unit is small. Accordingly, there is a possibility that memory cells can be further scaled-down.
Many organic molecules used for charge storage layers are polycyclic derivatives such as porphyrin having stable redox reactions. However, those organic molecules have steric hindrance. So, the molecular density is not sufficiently high in fabrication of self-assembled monolayer. Furthermore, formation of high steric hindrance molecule might be low orientation, even if that molecule have high orientaional portions such as long-alkyl chain. Therefore, it is difficult to increase the density of stored charges and secure a sufficient data retention time.